Novel phosphorous-nitrogen compounds used as fireproofing agents in theroplastic molding materials and the production thereof

ABSTRACT

In the process for preparing phosphorus-nitrogen compounds by reacting phosphorus sulfides with an amino component which  
     has at least one nitrogen atom having at least two hydrogen atoms, or  
     has at least two nitrogen atoms having at least one hydrogen atom,  
     the desired phosphorus-nitrogen compounds are formed at a temperature T max ≧200° C.  
     These compounds are preferably used as flame retardants in thermoplastic molding compositions which then may also comprise, inter alia, besides a thermoplastic polymer,  
     a nitrogen compound,  
     fillers,  
     lubricants,  
     conventional additives, and/or  
     conventional impact modifiers.

[0001] The invention relates to novel phosphorus-nitrogen compounds, toa process for their preparation, to their use as flame retardants inthermoplastic molding compositions, and also to thermoplastic moldingcompositions comprising these novel phosphorus-nitrogen compounds.

[0002] From the reaction of urea with phosphorus pentasulfide C. V.Kutschig (Monatsh. Chem. 9 (1888) 406 to 413) and F. V. Hemmelmayr(Monatsh. Chem. 26 (1905) 765 to 782) obtained the phosphorus-nitrogencompound ammonium4,6-dioxo-2-thiooxohexahydro-1,3,5,2-λ⁵-triazaphosphorinane-2-thiolate.Here, the reaction of urea with phosphorus pentasulfide took place witha molar ratio P₄S₁₀ to urea of 1:3.7 on a boiling waterbath, i.e. atfrom 80 to 90° C. The product obtained was highly soluble in hot waterand had a decomposition temperature of 230° C.

[0003] U.S. Pat. No. 4,061,589 discloses the use of 1,3,5-triazine4,6-diketo 2-dithio ammonium phosphamate and 1,3,5-triazine 4,6-dithio2-dithio ammonium phosphamate as corrosion inhibitors in cooling-watersystems. These phosphorus-nitrogen compounds are prepared by reactingurea compounds with phosphorus pentasulfide at 100° C. The product isobtained by extraction with cold water and decomposes above 260° C.

[0004] DE-A 24 17 991 relates to the preparation of thiophosphoramides,which are used as antioxidants for polymers. They are prepared byreacting phosphorus pentasulfide with primary or secondary aromaticamines at from 100 to 150° C., followed by addition of aliphatic oraromatic alcohol or amine at from 100 to 150° C. in an organic solvent.The thiophosphoramides are obtained by crystallization after distillingoff the organic solvent.

[0005] DD-A 203 724 relates to the preparation of ammonium4,6-dioxo-2-thiooxohexahydro-1,3,5,2-λ⁵-triazaphosphor-inane-2-thiolatefrom phosphorus pentasulfide and urea at from 90 to 130° C. The yield ofdesired product is temperature-dependent, the yield increasing at highertemperatures. However, the spontaneous decomposition of urea begins at140° C., reducing the yield. The products obtained are used asintermediates for preparing biocides or as constituents of lubricants orof corrosion inhibitors.

[0006] It is an object of the present invention to prepare novelphosphorus-nitrogen compounds which, when compared with thephosphorus-nitrogen compounds known from the prior art have inparticular low water-solubility and high thermal stability. The novelphosphorus-nitrogen compounds are to be suitable as flame retardants forthermoplastic molding compositions.

[0007] We have found that this object is achieved using a process forpreparing phosphorus-nitrogen compounds by reacting phosphorus-sulfideswith an amino component which

[0008] has at least one nitrogen atom having at least two hydrogenatoms, or

[0009] has at least two nitrogen atoms having at least one hydrogenatom.

[0010] The novel process then comprises forming the desiredphosphorus-nitrogen compounds at a temperature T_(max)≧200° C.

[0011] This temperature T_(max) is the highest temperature arising inthe novel process. When carrying out the novel process in more than onestage, the temperature T_(max) is reached here in at least one stage.The temperature T_(max) is preferably from 200 to 350° C., particularlypreferably from 280 to 320° C.

[0012] The phosphorus-nitrogen compounds obtained with the aid of thenovel process have high thermal stability. This means that nodecomposition is observed over a period of at least 15 min. attemperatures within the range from, in general, room temperature to 300°C.

[0013] At the same time, the phosphorus-nitrogen compounds prepared bythe novel process have very low water-solubility. The water solubilityof these compounds is generally from 0 to 5 g/l, preferably from 0 to0.5 g/l, particularly preferably from 0 to 0.1 g/l. Thephosphorus-nitrogen compounds are therefore particularly suitable foruse in locations where resistance to moisture is a major requirement.

[0014] Without adopting any particular theory, the low water-solubilitymay be due to the formation of highly crosslinked polymeric structuresin the phosphorus-nitrogen compounds obtained according to theinvention. The formation of the highly crosslinked polymeric structuresis a result of the high temperatures T_(max) used in the novel process.In cases where the amino components used have two or more hydrogen atomsbonded to one nitrogen atom, crosslinking can take place to give highlycrosslinked phosphorus-nitrogen compounds with development of P—N—(R)—Pbridges. In cases where the amino components used have at least twonitrogen atoms with at least one hydrogen atom bonded to each of these,the crosslinking also takes place via the molecular chain of the aminocomponent with development of P—N—R—N—P bridges. For the purposes of thepresent invention, R here is a molecular moiety corresponding to theradical of the respective amino component used.

[0015] The amino component used in the novel process has preferably beenselected from primary aliphatic or aromatic amines, primary or secondarydiamines, diimines, primary or secondary ammonium salts, amides oforganic or of inorganic acids, hydrazines, hydrazides, semicarbazides,semicarbazones, urea, dicyandiamide, melamine, guanidine or its salt(guanidinium carbonate) or mixtures of these.

[0016] Particularly suitable examples of the appropriate groups aregiven below:

[0017] Primary Aliphatic or Aromatic Amines

[0018] R¹=H or an aliphatic or aromatic organic radical preferablyhaving from 1 to 12 carbon atoms.

[0019] Primary or Secondary Diamines

[0020] R² and R³=H or an aliphatic or aromatic organic radicalpreferably having from 1 to 12 carbon atoms.

[0021] R⁴=a hydrocarbon chain preferably having from 1 to 12 carbonatoms.

[0022] Diimines

[0023] R⁵ and R⁶=H or an aliphatic or aromatic organic radicalpreferably having from 1 to 12 carbon atoms.

[0024] R⁷=a hydrocarbon chain preferably having from 1 to 12 carbonatoms.

[0025] Primary or Secondary Ammonium Salts

[0026] R⁸ and R⁹=H or any desired aliphatic or aromatic organic radicalpreferably having from 1 to 12 carbon atoms.

[0027] X=any desired anion, preferably halogen-free.

[0028] Amides of Organic or of Inorganic Acids (e.g. Carboxamides orSulfonamides)

[0029] R¹⁰ and R¹¹=H or any desired aliphatic or aromatic organicradical preferably having from 1 to 12 carbon atoms.

[0030] Hydrazines

[0031] R¹², R¹³, R¹⁴ and R¹⁵=H or any desired aliphatic or aromaticorganic radical preferably having from 1 to 12 carbon atoms.

[0032] Hydrazides

[0033] R¹⁶ and R¹⁷=H or any desired aliphatic or aromatic organicradical preferably having from 1 to 12 carbon atoms.

[0034] Semicarbazides

[0035] R¹⁸, R¹⁹, R²⁰, R²¹ and R²²=H or any desired aliphatic or aromaticorganic radical preferably having from 1 to 12 carbon atoms.

[0036] Semicarbazones

[0037] R²³, R²⁴ and R²⁵=H or any desired aliphatic or aromatic organicradical preferably having from 1 to 12 carbon atoms.

[0038] Guanidine, e.g. in the Form of its Salt Guanidinium Carbonate

[0039] It is preferable to use amino components selected from urea,dicyandiamide, melamine, guanidine or its salt, in particularguanidinium carbonate, or mixtures of these.

[0040] The phosphorus sulfides used are preferably monomeric phosphorussulfides of composition P₄S_(n), where n is from 3 to 10, or mixtures ofthese. Use of P₄S₁₀ or P₄S₃ is preferred, and use of P₄S₁₀ isparticularly preferred. For the purposes of the present invention, P₄S₁₀(tetraphosphorus decasulfide) is the same compound as phosphoruspentasulfide (P₂S₅). The form in which this substance in present as asolid is P₄S₁₀, it melts at 288° C. and boils at 514° C., forming ayellow vapor composed of molecules whose mass corresponds to P₂S₅.

[0041] The phosphorus sulfides used in the novel process may be preparedin an upstream reaction, by melting red phosphorus and sulfur togetherin a carbon dioxide atmosphere. This usually gives mixtures of differentphosphorus sulfides which, without any further purification orseparation, can be reacted with the amino component. It is also possiblefor the appropriate phosphorus sulfide or the phosphorus sulfidemixtures to be formed in situ during the reaction with the aminocomponent.

[0042] The ratio of the sulfur atoms present in the phosphorus sulfidesto the condensable nitrogen groups present in the amino components isgenerally from 1:0.5 to 1:10, preferably from 1:1 to 1:5, particularlypreferably from 1:2 to 1:3. This ratio of sulfur atoms to condensablenitrogen groups gives a particularly high degree of crosslinking in thedesired phosphorus-nitrogen compounds and thus very low water-solubilityin these compounds. Depending on the ratio of the appropriate phosphorussulfide to the amino component used, and on the reaction temperature,the sulfur may be completely or to some extent eliminated during thecondensation in the form of gaseous compounds, e.g. H₂S, COS and/or CS₂,or in the form of sublimable compounds. The novel process, which iscarried out at ≧200° C. therefore gives a water-insoluble product with alow residual sulfur content.

[0043] The reaction of the novel process generally takes place in aninert gas atmosphere. For the purposes of the present invention, inertgas is any gas which does not enter into any chemical reaction with thestarting materials, intermediates or final products. Suitable inertgases are Ar, N₂, He and CO₂, particularly preferably N₂.

[0044] In one preferred embodiment the novel process embraces thefollowing steps:

[0045] a) heating the phosphorus sulfide and the amino componenttogether to the temperature T₁ under an inert gas, and

[0046] b) slowly heating the resultant reaction mixture to T_(max)≧200°C. under an inert gas.

[0047] The temperature T₁ in step a) is generally from 90 to 300° C.,preferably from 95 to 250° C., particularly preferably from 180 to 250°C. During the reaction there is usually some evolution of gas, e.g. H₂S,COS and/or CS₂. The end of step a) can be recognized by the cessation ofthis gas evolution. The reaction times here depend, inter alia, on thefeed rate of the amino component.

[0048] The reaction mixture obtained at the end of step a) is usuallysolid.

[0049] In the following step b), the resultant reaction mixture, ifdesired comminuted, is annealed at a temperature T_(max)≧200° C.,preferably from 200 to 250° C., particularly preferably from 280 to 350°C.

[0050] Step b) is carried out under one of the abovementioned inertgases.

[0051] Any odor of hydrogen sulfide which may attach to the resultantphosphorus-nitrogen compounds, depending on their sulfur content, may beremoved by adding in general from 2 to 20% by weight, preferably from 5to 15% by weight, of zinc oxide in step b). Adding zinc oxide does notimpair the properties of the phosphorus-nitrogen compounds, inparticular their flame retardancy.

[0052] Another way of removing any odor attaching to thephosphorus-nitrogen compounds is to oxidize the phosphorus-nitrogencompounds with an oxidizing gas, such as air, oxygen, NO₂, preferablyair, at in general from 50 to 300° C., preferably at from 100 to 300° C.

[0053] Any commonly used type of reactor is generally suitable as areaction vessel for carrying out the process of the invention.Particular preference is given to a mixing vessel with a stirrer whichpasses close to the wall, and to paddle dryers and Diskotherm reactors,by means of which the product which forms, where appropriate as a solid,can also be ground and homogenized as the reaction in step a) proceeds.

[0054] The present invention also provides phosphorus-nitrogen compoundswhich can be prepared by the process of the invention. These compoundshave high thermal stability, and also low water-solubility.

[0055] They are highly suitable for use as flame retardants, inparticular in thermoplastic molding compositions. The present inventiontherefore also provides the use of the phosphorus-nitrogen compounds ofthe invention as flame retardants in thermoplastic molding compositions.

[0056] There is a major requirement for halogen-free flame retardantssuch as the phosphorus-nitrogen compounds of the invention, since thehalogen-containing flame retardants commonly used can release toxicand/or corrosive compounds in the event of a fire, for example dioxinsand halogenated hydrocarbons. Red phosphorus, which is commonly used,has the disadvantage of intrinsic color.

[0057] The high thermal stability of the phosphorus-nitrogen compoundsof the invention, which do not decompose over a period of at least 15minutes at in general up to 300° C., means that the compounds can beincorporated into high-melting molding compositions, such as nylon-6,6and polybutylene terephthalate without any decomposition of thephosphorus-nitrogen compounds.

[0058] The phosphorus-nitrogen compounds of the invention also have apale instrinsic color, and the color of the desired final products istherefore not impaired by incorporating the phosphorus-nitrogencompounds of the invention. The polymer-compatibility of thephosphorus-nitrogen compounds of the invention is high, and thecompounds are therefore distributed uniformly within the thermoplasticmolding compositions.

[0059] The phosphorus-nitrogen compounds of the invention are effectiveboth in unreinforced polymers and in polymers reinforced with fillers.One of the reasons for the high effectiveness of the phosphorus-nitrogencompounds of the invention is their high phosphorus-nitrogen content,which is in total generally >50%, preferably >55%, particularlypreferably >60%, but at least 35%.

[0060] Another advantage of the phosphorus-nitrogen compounds of theinvention when used as flame retardants in thermoplastic moldingcompositions is their very low water-solubility.

[0061] This prevents elution or migration of the flame retardant, inparticular when products produced from the thermoplastic moldingcompositions comprising the phosphorus-nitrogen compounds are used inconditions of wet weathering. Oxidation and/or hydrolysis of any flameretardant used in the thermo plastic molding compositions could lead topartial breakdown of the thermoplastic molding compositions, but theseprocesses can be avoided by using the phosphorus-nitrogen compounds ofthe invention.

[0062] When used as flame retardants, the phosphorus-nitrogen compoundsof the invention are suitable for incorporation into any desiredthermoplastic polymer.

[0063] The present invention therefore also provides thermoplasticmolding compositions comprising:

[0064] a) from 5 to 99% by weight, preferably from 10 to 80% by weight,particularly preferably from 30 to 80% by weight, of a thermoplasticpolymer, as component A,

[0065] b) from 1 to 40% by weight, preferably from 5 to 35% by weight,particularly preferably from 10 to 30% by weight, of aphosphorus-nitrogen compound of the invention, as component B,

[0066] c) from 0 to 30% by weight, particularly preferably up to 20% byweight, of a nitrogen compound, as component C,

[0067] d) from 0 to 50% by weight, preferably from 1 to 50% by weight,particularly preferably from 20 to 40% by weight, of fillers, ascomponent D,

[0068] e) from 0 to 5% by weight, preferably from 0.01 to 3% by weight,of lubricants, as component E,

[0069] f) from 0 to 10% by weight, preferably up to 8% by weight,particularly preferably up to 3% by weight, of conventional additives,and

[0070] g) from 0 to 30% by weight, preferably up to 25% by weight,particularly preferably up to 20% by weight, of conventional impactmodifiers, as component G.

[0071] Component A

[0072] Suitable thermoplastic polymers are either polycondensates orelse polymers or polyadducts. Suitable thermoplastic polycondensates arepolyamides, particularly preferably nylon 6,6, nylon-6, nylon-11,nylon-12, nylon-4,6, and also copolyamides, such as nylon-6/6T,nylon-6,6/6T, and polyamides built up from caprolactam and hexamethyleneadipamide and, if desired, from another comonomer. Other suitablethermoplastic polycondensates are polycarbonates, polyesters, preferablypolyterephthalates, such as polyethylene terephthalate or polybutyleneterephthalate, polyphenylene oxides, polysulfones and polyvinylacetates. Suitable thermoplastic polymers are polyolefins, in particularpolyethylene, polypropylene, poly-1-butene, poly-4-methyl-1-pentene, andalso polyvinyl chloride, polyvinylidene chloride, polymethylmethacrylate, polyacrylonitrile, polystyrene, impact-modifiedpolystyrene, polyacetals, polyvinyl alcohols, polyvinyl acetate andpoly-p-xylylene. Suitable thermoplastic polyadducts are linearpolyurethanes. Component A is particularly preferably a thermoplasticpolycondensate, in particular a polyamide or a polyester. It is veryparticularly preferably nylon-6,6, nylon-6, nylon-6/6T, nylon-6,6/6T,nylon-6/6,6 or polyethylene terephthalate or polybutylene terephthalate.Nylon-6,6, nylon-6, nylon-6/6,T, nylon-6,6/6,T, nylon-6/6,6 and alsopolyethylene terephthalate and polybutylene terephthalate are relativelyhigh-melting polymers. Processing to give thermoplastic moldingcompositions therefore requires the use of components which do notdecompose at the high process temperatures required. Thephosphorus-nitrogen compounds of the invention, which are thermally verystable, are therefore highly suitable for use as flame retardants inthermoplastic molding compositions of this type.

[0073] Other suitable thermoplastic polymers are styrene-acrylonitrilecopolymers (SAN), α-methylstyrene-acrylonitrile copolymers,styrene-methyl methacrylate copolymers and styrene-maleic anhydridecopolymers, and also acrylonitrile-butadiene-styrene polymers (ABS) andacrylonitrile-styrene-acrylate polymers (ASA).

[0074] Component B

[0075] Component B is a phosphorus-nitrogen compound of the invention,which can be prepared by the process of the invention.

[0076] Component C

[0077] Component C is a nitrogen compound selected from guanidine salts,allantoin compounds, ammonium polyphosphates, melamine and melaminecompounds, preferably melamine cyanurate.

[0078] Component D

[0079] Suitable fillers are carbonates, in particular calcium carbonate,silicates, such as talc, clay and mica, siliceous earth, calciumsulfate, barium sulfate, aluminum hydroxide, glass fibers and glassbeads, and also wood flour and cellulose powder.

[0080] Component E

[0081] Particularly suitable lubricants are fatty amides and fattyesters, which may in each case be mono- or polyfunctional, salts offatty acids, preferably zinc salts of fatty acids or calcium stearate,salts or esters of montanic acid, esters of montanic acid beingpreferred, in particular those having C₁₂-C₁₆-alkyl chains, andpolyalkylene waxes and modified alkylene waxes, in particularpolyethylene waxes and partially oxidized polyethylene waxes.

[0082] Component F

[0083] Commonly used additives are stabilizers, nucleating agents,pigments, dyes, plasticizers and antidrop agents.

[0084] Component G

[0085] Particularly suitable commonly used impact modifiers areethylene-propylene rubber (EPM) and ethylene-propylene-diene rubbers(EPDM), in each case preferably grafted with reactive groups (carboxylicacids, anhydrides) and also copolymers of ethylene with acrylic acidand/or methacrylic acid and/or with esters of these acids.

[0086] The thermoplastic molding compositions may be prepared by mixingcomponents A and B and also, if desired, C to G at elevatedtemperatures, thus melting component A. These thermoplastic moldingcompositions comprising the phosphorus-nitrogen compounds of theinvention as flame retardants may be used to produce moldings, films orfibers.

[0087] Use of the phosphorus-nitrogen compounds of the invention asflame retardants in thermoplastic molding compositions is compliant withthe flame retardancy requirements at least of UL 94 V-2, preferably UL94 V-0. UL here means Underwriters Laboratories, V-2 means an afterflametime per flame application of ≦30 s and a total afterflame time for 10flame applications of ≦250 s. V-0 means an afterflame time per flameapplication of ≦10 s and a total afterflame time of ≦50 s. V-1 (seeTable 1) means the same afterflame time and total afterflame time as forV-2 but no formation of flaming drops.

[0088] The examples below further illustrate the invention.

EXAMPLES

[0089] Preparation of the Phosphorus-Nitrogen Compounds

Example 1

[0090] A mixture of 200 g of phosphorus pentasulfide and 270 g of ureawas heated in a glass flask under nitrogen at 235° C. for 5 hours.During this process a homogeneous melt was first formed, with evolutionof gas, and at increased temperature this foamed with vigorous evolutionof gas and became solid. After cooling, the reaction product was groundand annealed for 5 hours under nitrogen at 350° C. This gave 199 g ofproduct (24.8% by weight phosphorus, 37.7% by weight nitrogen, 20.8% byweight oxygen, 12.0% by weight carbon, 0.3% by weight sulfur). After 5hours the solubility in water was 0.81 g/1000 g.

Example 2

[0091] A mixture of 240 g of phosphorus pentasulfide and 454.2 g ofdicyandiamide was heated in a glass flask under nitrogen at 96° C. for15 minutes. During this process a foam-like mass was formed, and rapidlyhardened. After cooling, the product was ground and slowly heated to350° C. under nitrogen and annealed for 8 hours at 350° C. This gave 439g of product (13.8% by weight phosphorus, 55.9% by weight nitrogen,21.9% by weight carbon, 4.6% by weight sulfur). After 5 hours thesolubility in water was 0.17 g/1000 g.

Example 3

[0092] 100 g of phosphorus pentasulfide in a paddle drier (volume 0.77l) were preheated to 200° C. A total of 188 g of dicyandiamide were thenfed in portions over a period of 3.5 hours. The reaction temperaturehere was 250° C. Once the reaction had ended, 10 g of zinc oxide wereadded and the product annealed for 2 hours at 300° C. This gave 143 g ofproduct.

[0093] Use of the Resultant Phosphorus-Nitrogen Compounds as FlameRetardants

[0094] The components were mixed in a twin-screw extruder at 280° C.(nylon-6,6) or 260° C. (polybutylene terephthalate). For the UL 94 firetests, fire specimens of thickness 1.6 mm were injection molded. Thefire tests were carried out to the UL specification after the usualconditioning (2 days at 23±2° C. and atmospheric humidity of 50±5% and 7days at 70±1° C. and then cooling in a dessicator). For the tests, 5fire specimens were each exposed twice for 10 s to flame applicationfrom a gas burner (flame height 20±1 mm) and the afterflame timemeasured.

[0095] Components:

[0096] Component A1:

[0097] Nylon-6,6 with a viscosity number of 147 ml/g (measured with anUbbelohde capillary viscometer in 0.5% strength solution in 96% strengthH₂SO₄).

[0098] Component A2:

[0099] Polybutylene terephthalate with a viscosity number of 130 ml/g(measured with an Ubbelohde capillary viscometer in 0.5% strengthsolution in dichlorobenzene/phenol 1/1).

[0100] Component B1:

[0101] Phosphorus-nitrogen compound based on Synthesis Example 1.

[0102] Component B2:

[0103] Phosphorus-nitrogen compound based on Synthesis Example 2.

[0104] Component B3:

[0105] Phosphorus-nitrogen compound based on Synthesis Example 3.

[0106] Component B4 (Comparative Experiment):

[0107] Melamine polyphosphate (Melapur P200, from DSM Melapur)

[0108] Component C:

[0109] Melamine cyanurate.

[0110] Component D:

[0111] Chopped glass fiber of thickness 10 μm. 1 2 3 4 (c)¹ 5 6 7 A1 5555 55 55 (% by weight) A2 50 50 50 (% by weight) B1 20 25 (% by weight)B2 20 20 10 % by weight) B3 20 % by weight) B4 20 (% by weight) C 10 (%by weight) D 25 25 25 25 25 30 30 (% by weight) UL 94 V-0 V-0 V-0 V-1V-2 V-2 V-2 1.6 mm

We claim:
 1. A process for preparing phosphorus-nitrogen compounds byreacting phosphorus sulfides with an amino component which has at leastone nitrogen atom having at least two hydrogen atoms, or has at leasttwo nitrogen atoms having at least one hydrogen atom, which comprisesforming the desired phosphorus-nitrogen compounds at a temperatureT_(max)≧200° C.
 2. A process as claimed in claim 1, wherein the aminocomponent has been selected from primary aliphatic or aromatic amines,primary or secondary diamines, diimines, primary or secondary ammoniumsalts, amides of organic or inorganic acids, hydrazines, hydrazides,semicarbazides, semicarbazones, urea, dicyandiamide, melamine, guanidineor its salt, or mixtures of these.
 3. A process as claimed in claim 2,wherein the amino component has been selected from urea, dicyandiamide,melamine, guanidine or mixtures of these.
 4. A process as claimed in anyone of claims 1 to 3, wherein use is made of monomeric phosphorussulfides of composition P₄S_(n), where n is from 3 to 10, or mixtures ofthese.
 5. A process as claimed in claim 4, wherein the phosphorussulfide is P₄S₁₀.
 6. A process as claimed in any one of claims 1 to 5,wherein the ratio of sulfur atoms present in the phosphorus sulfides tocondensable nitrogen groups present in the amino component is from 1:0.5to 1:10.
 7. A process as claimed in any one of claims 1 to 6, embracingthe following steps: a) heating the phosphorus sulfide and the aminocomponent together to the temperature T₁ under an inert gas, and b)slowly heating the resultant reaction mixture to T_(max)≧200° C. underan inert gas.
 8. A process as claimed in claim 7, wherein step b) iscarried out with addition of from 2 to 20% by weight of zinc oxide.
 9. Aphosphorus-nitrogen compound which can be prepared by a process ofclaims 1 to
 8. 10. The use of a phosphorus-nitrogen compound as claimedin claim 9 as flame retardant in thermoplastic molding compositions. 11.A thermoplastic molding composition comprising: a) from 5 to 99% byweight of a thermoplastic polymer, as component A, b) from 1 to 40% byweight of a compound as claimed in claim 9, as component B, c) from 0 to30% by weight of a nitrogen compound, as component C, d) from 0 to 50%by weight of fillers, as component D, e) from 0 to 5% by weight oflubricants, as component E, f) from 0 to 10% by weight of conventionaladditives, as component F, and g) from 0 to 30% by weight ofconventional impact modifiers, as component G.
 12. A process forpreparing a thermoplastic molding composition as claimed in claim 11,which comprises mixing components A and B and also, if desired, C to Gat an elevated temperature, with melting of component A.
 13. The use ofa thermoplastic molding composition as claimed in claim 11 for producingmoldings, films or fibers.